Objective To determine the association between socioeconomic factors and the prevalence of asthma according to two different definitions.
Method 1681 children (7–11 years) from two Brazilian cities: Ribeirão Preto (RP) a developed city and São Luís (SL), a less developed location, were investigated for current asthma symptoms, defined as the presence of whistling sounds or wheezing in the last 12 months. An objective measure (bronchial hyperresponsiveness; BHR) was assessed in 773 children. Positive BHR was defined as methacholine PC20 less than 2 mg/ml. The association of each asthma definition with each socioeconomic factor was assessed using multiple logistic regressions, adjusted for city and gender.
Results The prevalence of asthma symptoms was 18.3% in RP and 20.0% in SL (p = 0.424). The prevalence of positive BHR plus symptoms was higher in the most developed city (12.2% vs 8.0%), a marginally significant result (p = 0.091). A protective effect against asthma symptoms was found in children with higher family income (odds ratio (OR) 0.51; 95% CI 0.34 to 0.77), whose head of the family’s occupation was non-manual (OR 0.58; 95% CI 0.38 to 0.89) and whose mothers had a higher educational level (OR 0.66; 95% CI 0.49 to 0.91). Increased asthma symptoms were found among children from lower economic groups (OR 2.03; 95% CI 1.30 to 3.19). None of the factors analysed showed statistically significant association with asthma defined as current symptoms plus positive BHR.
Conclusion Asthma symptoms predominated among low socioeconomic groups. However, when an objective measure (BHR) was added no socioeconomic variation was found. The association between socioeconomic measures and asthma symptoms may be due to report bias.